Fatigue has been implicated in 234 Air Force Class A mishaps, 27 of which have fatigue as a causal factor. As the Air National Guard continues to do more with less, it is vital to address the issue of fatigue in aviation operations. Sustained night-time combat operations must take fatigue into account—a single night without sleep with today's sophisticated aircraft can result in the loss of enough higher cognitive function to be fatal.
Between 1974 and 1992, 25% of the Air Force's night tactical fighter Class A accidents were attributed to fatigue. Over 12% of the Navy's total Class A accidents between 1977 and 1990 were thought to be the result of aircrew fatigue. Some reports have put the annual cost of fatigue-related Air Force mishaps as high as $45M, in addition to loss of lives. Note the crash of Korean Air flight 801 in which 228 people died; the near crash of China Airlines flight 006 in which two people were severely injured and other passengers were traumatized; or the accident involving American Airlines 1420 in which 11 people died. In each of these cases, crew fatigue from long duty periods and/or circadian factors have been implicated. (AFRL 2003-0059) Fatigue has been implicated in the Three Mile Island accident, Exxon Valdez environmental spill, and Chernobyl nuclear plant disaster.
NASA's Michael Mann, on the August 1999 Pilot Fatigue hearing to the Aviation Subcommitee, United States House of Representatives, testified that “ . . . pilot fatigue is a significant safety issue in aviation. Rather than simply being a mental state that can be willed away or overcome through motivation or discipline, fatigue is rooted in physiological mechanisms related to sleep, sleep loss, and circadian rhythms.” The FAA has reported that 21% of the error reports in NASA's confidential Aviation Safety Reporting System reference fatigue as a direct or indirect factor.
Fatigue drives breakdowns in crew resource management, shortens attention spans, increases susceptibility to spatial disorientation, and causes deadly microsleep events in crews on final approach and landing. Loss of performance due to sleep deprivation follows extremely closely with loss of performance from blood alcohol content; 24 hours wakefulness approximates to 0.10 BAC, a level considered legally drunk in most states. Yet our crews routinely take off in the evening and head across the Atlantic, landing a complex, multi-million dollar aircraft after being up all night.
A significant step in fatigue management is the introduction of computer-based tools which intend to predict, for example, human aviator performance. These automated tools employ human sleep models and their relationship to cognitive performance. To date, however, such tools' interfaces are difficult to use, time consuming, and do not address specific concerns for different airframes and mission profiles, and ultimately, are only as good as the sleep models employed.
The original implementation of prior art fatigue calculation methods was based on the Warfighter Fatigue Model paper written by Dr. Steven Hursh et al. The paper describes the Sleep, Activity, Fatigue, and Task Effectiveness (SAFTE) model. This can be thought of as a mathematical simulation based on a rising and falling reservoir. When an individual is awake, the reservoir slowly depletes, and when the individual is asleep, the reservoir level rises. In conjunction with this process, biological circadian rhythms are taken into account along with jet lag to determine an individual's effectiveness at any given time. However, the prior art SAFTE model by itself did not provide or consider any methods for automatically adding sleep to work schedule, it did not provide a method for introducing multiple sleep models representative of the different possible modes of sleep, nor did it provide a method for introducing and analyzing the influence of secondary factors such as stimulants, sleep inertia, etc on crew effectiveness.
Another prior art fatigue monitoring system called FAST did not provide any means for accounting the effects of jet lag, time zone shifts, or many other factors today deemed highly relevant.
There exists a great and urgent need for proactive, rather than reactive approaches to aircrew shift fatigue monitoring, allowing the military flight planner the flexibility to not only automatically factor the benefits of the additions of sleep into a shift work schedule so as to optimize worker effectiveness, but also to account for the effects of various sleep modes and other effects associated with travel across multiple time zones and the resultant performance when planning flying operations.